Polypropylene carpet fibers



United States Patent 3,286,322 POLYPROPYLENE CARPET FIBERS Loy D.Sneary, Bartlesville, Okla, assignor to Phillips Petroleum Company, acorporation of Delaware No Drawing. Filed Aug. 5, 1963, Ser. No. 300,0812 Claims. (Cl. 28-76) This invention relates to textile carpets madewith polypropylene fibers. In another aspect it relates to providing acarpet of superior tuft resilience woven from polypropylene fiber.

Thermoplastics have been considered, and certain types developed, as asource of textile fibers, but they have also been found to presentproblems which were long ago solved with the older cellulosicfibers.Polyolefins, among other thermoplastics, because of their chemicalresistivity are a class of textile yarns of highly desirable properties,if the physical processing requirements can be attained. .Polyolefinscan be readily prepared as a continuous single filament by extrusionfrom a polymer melt through a die. It is then possible to form amultifilament yarn therefrom in many textile applications.

One of the main drawbacks with natural fibers and conventionallyprepared polyolefin fibers has been their lack of long-term resiliencewhen employed in carpets. Typically, a polyolefin staple yarn, or bulkedcontinuous filament yarn, when manufactured by conventional methods,tends to pack down after as little as several days of depression underfurniture legs, and the like, retaining an unsightly permanent set whenthe furniture is moved. It is hypothesized that this may occur because,under a long-term load, the polyolefin molecules and/or crystallitestend to slip past one another leading to a more or les's permanentdeformation.

The prior art has suggested the use of ionizing radiation, such as highenergy electrons, to cause cross-linking in formed polyethylene and givea less'deformable plastic shape. It should be noted, however, that theuse of ionizing radiation is relatively expensive, difiicult to control,and being hazardous, requires considerable safeguards.

The cross-linking of polyethylene with radiation has been extensivelystudied; it is known to be a polymer of the cross-linking type with ascission-to-crosslinking ratio of about 0.35. Radiation affectspolypropylene quite differently than it does polyethylene. Whereas thecrosslinking-to-scission ratio is favorable for crosslinking ofpolyethylene, it is very close to unity for polypropylene, and yields avery low efficiency for the crosslinking of the latter under straightradiation-crosslinking. The dose required [501 incipient Igelaition(indicative of crosslinking) of polypropylene, for example, is reportedto be about 50 megarads even though this dose has been decreased withannealing techniques. Keeping in mind the expense of high energyradiation, the cross-linking of formed polypropylene by this methodwould appear economically prohibitive.

It has been discovered that in order to economically cross-linkpolypropylene, it is first necessary to incorporate a cross-linking aid,specifically a polyfunctional monomer, into the polypropylene yarn,which monomer cross-links upon exposure to radiation and gives a fiberof significantly greater resilience, and thus improved resistance topermanent deformation under load than unmodified polypropylene fiber.

According to the present invention, a conventionally manufacturedpolypropylene continuous filament, or staple yarn is first bulked, e.g.by crimping, to give a bulked yarn, and then may be cross-linked by amethod which comprises: immersing the yarn in a bath of a polyfunctionalmonomer selected from the .group consisting of divinyl'benzene, themono-, di-, triand tetraethylene glycol diacrylates, the mono-, di-,triand tetra-ethylene glycol dimethacrylates, vinyl acrylate, vinylmethacrylate, allyl acrylate, allyl methacrylate, the divinyl ether ofdiethylene glycol, diallyl maleate, diallyl i-taconate,- diallylmalonate, diallyl benzene phosph-onate, triallyl phosphate, triallylcyanurate, glyceryl trimethacrylate; subsequently exposing themonomer-saturated yarn to a field of high energy radiation for a timesuificient to give superior resilience to said yarn by cross-linking ofsaid monomer-polymer components. The immersion may occur after as wellas before the bulking step.

Fibers, especially the monofilaments used in my invention, have adiameter of 0.1 to 50 mils and more usually about 0.5 to 3 mils. Thetensile strength of these fibers oold dra'wn is above 30,000 psi,frequently above 90,000 to 100,000 psi. and can range as high as 150,000to 250,000 p.s.i. measured at a temperature in the range of 65 to F.

Practice of the present invention permits cross-linked polypropylenecompositions to be obtained with the litmost expedience and economy. Thesupplementing cross-linking effect of the absorbed copolymerizingmonomer permits a desired degree of cross-linking to be obtained in theresulting composition, with greatly reduced dependence upon the effectsand required quantities of the high energy radiation.

Generally, exceptionally satisfactory results can be achieved whendivinyl benzene, mono-, tri-, and tetraethylene glycol dimethacrylate,allyl acrylate and methacrylate, vinyl methacrylate and diallyl maleateare employed as the polyfunctional monomer to cross-link, or facilitatethe crosslinking of, [the polypropylene fiber that is utilized.Surprisingly enough, as is apparent from the foregoing, selection of thepolyfunctional monomer is relatively critical, and surprisingly'l'lOl'l-plBdiCta'bk. Random choice of many ostensibly similar orequivalent polyfunctional monomers generally is found to provideinexplicalbly unsatisfactory (or no) results.

The quantity of the polyfunctional monomer that is incorporated in thepolymer may not only depend upon the specific nature and characteristicsof the particular polypropylene that is intended to be cross-linked, aswell as the particular cross-linking efficiency of the polyfunctionalmonomer that is involved, but also upon the properties that may bedesired to be imparted in the resulting composition. The quantity of thepolyfunctional monomer that is employed should be adequate to secure thedesired extent of cross-linking in the polymeric composition, takinginto account the degree of cross-linking that will be directly inducedin the composition from its exposure to the radiant high energy whichserves to crosslink the starting polymer by graft copolymerization ofthe absorbed monomer.

Generally, a satisfactory result may be achieved when minor proportionsof the monomer are incorporated intimately in the polymer. In someinstances, very minor proportions may suflice, especially when lowlevels of cross-linking are desired in the composition. It is difiicultto generalize on the weight proportions that may be suitably utilized inall instances due, as may be readily appreciated, to the greatvariations that may be encountered in the equivalent weights of the manypolyfunctional monomers that may be utilized.

Broadly speaking, it is desirable to utilize such a quantity of themonomer as may be adapted to provide between one and about three hundredfunctional, cross-linking bridges per every three thousand carbon atomsin the chains of the polymer that is desired to be cross-linked. To theattainment of such ends, it may frequently be found Patented Nov. 22,1966 advantageous to incorporate an amount of the monomer in the polymerthat is between 1 and 40 percent by weight, based on the Weight of theresulting composition. An amount of the monomer that is between 3 and 10percent by weight may even be more advantageous for most crosslinkingpurposes.

The monomer may be intimately incorporated in the polymer in any otherdesired manner e.g., a vapor bath, prior to the mutual irradiation ofthe uniformly associated mixture. Thus, physical interblending meanssuch as may be achieved by any of a variety of conventional techniquesmay be utilized. In many instances, however, it may be convenient andquite suitable to incorporate a liquid monomer having a dissolving,plasticizing, or swelling influence on the polymer, by immersing thelatter in the former until a desired monomer content has been uniformlyattained.

The radiation which is employed for cross-linking the treated yarn ispreferably of the high energy ionizing radiation, such as provided bygamma rays, electrons, protons, and alpha particles. The preferred formof radiation is gamma rays. When gamma rays are employed, the dose ratecan be within the range between 1 10 and 1x 10 rads (the amount ofradiation per hour producing an absorption of 1 ergs/ gram) for asufficient length of time so that the total dosage received by the fiberis within the range between 0.05 megarad up to 50 megarads, preferablyin the range one to ten megarads. The total dosage necessary to form afiber of superior resilience is primarily a function of radiationsensitivity of the particular crosslinking aid undergoing irradiation,and can be determined empirically.

Any suitable source of gamma rays can be used, including such sources asspent fuel elements from nuclear reactors, radioactive isotopes, cathodetubes, and linear accelerators employing targets such as tungsten forthe conversion of electrons to gamma rays.

If electrons, protons, or alpha particles are employed, the polymer issubjected to these particles having energies of from 1 million electronvolts (mev.) to 1 billion electron volts (bev.) and can be supplied fromsuch sources as linear accelerators, Van de Graft generators, betatrons,cyclotrons, and the like. Beam currents from these sources will rangefrom 0.1 to 1000 microamperes, and the irradiation time using such beamswill vary from 0.5 to 60 minutes.

Textile crimping involves continuously pressing the filament or towthrough a stufiing box, thereby compressing the material and givingcreases thereto, which give bulk to the thus treated material. Otherconventional bulking techniques, coiling, curling and looping, mayreadily be employed.

The fibers can, of course, be dyed to any of a variety of colors bymethod recently disclosed in the art.

The polypropylene yarns treated according to the method of thisinvention are now suitable for weaving into fine carpets on modern powerlooms. One of the principal varieties of carpets that can bemanufactured with polypropylene yarn is domestic Axminster. A firmground- Work of jute or cotton is employed, upon which the pilecontaining the design is fastened in tufts of soft polypropylene yarn.These tufts are supplied from a series of rollers corresponding innumber to the picks or wefts completing a pattern, and in length toWidth of the carpet, and are independent of the Warp and woof comprisingthe body of the fabric. This permits the employment of an almostunlimited number of colors and the most perfect and elegant designs.

Wilton carpets, another major type, are woven alike, and of the samematerials-line back and worsted face. The face of both is formed byinserting wires between the Warp threads in such a manner that on theirwithdrawal a series of raised loops of the worsted warp is formed, uponwhich the design appears. In the Wilton the pile is cut automatically inthe loom during the process of weaving. The worsted portion of thecarpet being exclusively in the warp, the threads of which are ofcontinuous color throughout the piece, each particular color requires aspecial set of threads, worked in an independent manner by what istechnically termed a frame. This arrangement secures great perfectionand clearness of design, for each color is brought to the surfaceentirely by itself, While the others are carried thru or under the linenback. The Work has the appearance of embroidery on canvas. For a moredetailed description of carpet weaving, see Encyclopaedia Brittanica,1953, volume 4, pages 917 to 922.

Example A polypropylene continuous filament yarn is prepared byconventional methods from pelleted polypropylene. The yarn is bulked bythe conventional crimping technique, to give a somewhat more resilientand bulky yarn. A skein of continuous yarn is immersed in a bath ofallyl methacrylate maintained at 25 C. for about 24 hours to achieve asaturation of about 4 percent by weight. The monomer-saturated yarn issubjected to gamma irradiation provided by a linear accelerator at fullpower (360 pulses per second), to produce a 3 kilowatt beam of electronson a tungsten target which converted to electrons to gamma rays. Theirradiation is continued for a period of time sufficient to give a totaldosage received of approximately 5 megarads. The resulting yarn whenincorporated into a conventional carpet structure will give greaterresilience under long term load than could be achieved by the prior artmethods.

Reasonable variation and modification are possible within the scope ofthe foregoing disclosure and appended claims.

I claim:

1. A method for providing a carpet of good tuft resilience woven fromfiber comprising: homopolymers and copolymers of propylene, whichcomprises:

(a) spinning polypropylene continuous filaments from polypropyleneresin;

(b) combining said filaments into continuous filament and staple yarns;

(c) bulking the resulting polypropylene yarn;

(d) immersing the bulked yarn in a bath of a polyfunctional monomer at atemperature between 20 and C. selected from the group consisting ofdivinyl benzene, the mono-, di-, triand tetra-ethylene glycoldiacrylates, the mono-, di-, triand tetra-ethylene glycoldimethacrylates, vinyl acrylate, vinyl methacrylate, allyl acrylate,allyl methacrylate, the divinyl ether of diethylene glycol, diallylmaleate, diallyl itaconate, diallyl malonate, diallyl benzenephosphonate, triallyl phosphate, triallyl cyanurate, glyceryltrimethacrylate;

(e) exposing the monomer-saturated bulked yarn to a field of high energyradiation for a time suflicient to give a total dosage within the rangebetween 0.05- and 50 megarads, thereby cross-linking of themonomet-polymer components thereof; and

(f) conventionally weaving the thus treated polypropylene yarn into acarpet.

2. A method for providing a carpet of good tuft re-- silience woven frompolypropylene fiber comprising:

(a) conventionally spinning polypropylene continuous:

filaments from polypropylene resin;

(b) combining said filaments into continuous filament and Staple yarns;

(c) crimping the resulting polypropylene fiber;

(d) immersing the crimped fiber in a bath of allyl methacrylate;

(e) exposing the monomer-saturated crimped fiber to a field of highenergy radiation for a time sufficient to give a total dosage within therange between 0.05 and 50'megarads and thereby impart resilience to saidfiber by cross-linking of the said monomer compo nent; and

. t 6 (f) conventionally Weaving the thus t r ated polyprbpyl- 3,131,9905/1964 Bpnviciniet 21. ene yarn into a carpet. 3,166,607 1/ 1965 Cerniaet a1. 3,188,165 6/1965 Magat et a1. References Cited by the ExaminerUNITED STATES PATENTS 5 FOREIGN PATENTS 2,999,056 9/1961 Tanner. 612,3191/1961 Canada" 3,019,507 2/1962 Maragliano et a1. 2872 836,254 6/1960Great m 3,049,507 8/1962 Stanton et al. 8441231 8/1960 Great m 3,049,5088/1962 Stahton et al. 919,071 2/1963 Great Bumm- 58,950 10/1962 Stantonntal. MERVIN STEIN, Primary Examiner. g gzgg g DONALD w. PARKER,Examiner. 3,101,522 8/1963 J. KEE CHI, Assistant Examiner.

Hooper et a1 2874

1. A METHOD FOR PROVIDING A CARPET OF GOOD TUFT RESILIENCE WOVEN FROMFIBER COMPRISING: HOMOPOLYMERS AND COPOLYMERS OF PROPYLENE, WHICHCOMPRISES: (A) SPINNING POLYPROPYLENE CONTINUOUS FILAMENTS FROMPOLYPROPYLENE RESIN; (B) COMBINING SAID FILAMENTS INTO CONTINUOUSFILAMENT AND STAPLE YARNS; (C) BULKING THE RESLUTING POLYPROPYLENE YARN;(D) IMMERSING THE BULKED YARN IN A BATH OF A POLYFUNCTIONAL MONOMER AT ATEMPERATURE BETWEEN 20* AND 120*C. SELECTED FROM THE GROUP CONSISTING OFDIVINYL BENZENE, THE MONO-, DI-, TRI- AND TETRA-ETHYLENE GLYCOLDIACRYLATS, THE MONO-, DI, TRI-AND TETRA-ETHYLENE GLYCOLDIMETHACRYLATES, VINYL ACRYLATE, VINYL METHACRYLATE, ALLYL ACRYLATE,ALLYL METHACRYLATE, THE DIVINYL ETHER OF DIETHYLENE GLYCOL, DIALLYLMALEATE, DIALLYL ITACONATE, DIALLYL MALONATE, DIALLYL BENZENEPHOSPHONATE, TRIALLYL PHOSPHATE, TRIALLYL CYANURATE, GLYCERYLTRIMETHACRYLATE; (E) EXPOSING THE MONOMER-SATURATED BULKED YARN TO AFIELD OF HIGH ENERGY RADIATION FOR A TIME SUFFICIENT TO GIVE A TOTALDOSAGE WITHIN THE RANGE BETWEEN 0.05 AND 50 MEGARADS. THEREBYCROSS-LINKING OF THE MONOMER-POLYMER COMPONENTS THEREOF; AND (F)CONVENTIONALLY WEAVING THE THUS TREATED POLYPROPYLENE YARN INTO ACARPET.